Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$72.32	4.859%	$75.834	$75.83	$75.85	$75.80
Purchase #2	$124.59	11.622%	$139.0698	$139.07	$139.05	$139.10
Purchase #3	$42.57	10.511%	$47.0445	$47.04	$47.05	$47.00
Purchase #4	$143.25	4.760%	$150.0687	$150.07	$150.05	$150.10
Purchase #5	$170.53	10.249%	$188.0076	$188.01	$188.00	$188.00
Purchase #6	$53.83	10.832%	$59.6609	$59.66	$59.65	$59.70
Purchase #7	$154.59	4.286%	$161.2157	$161.22	$161.20	$161.20
7 purchase totals =	$761.68		$820.9012	$820.90	$820.85	$820.90